Oil temperature sensors for detecting temperature of lubricating oil in an internal combustion engine are conventionally used to detect temperature of lubricating oil within a lubricating oil passage or within an oil pan. For example, in an internal combustion engine disclosed in Japanese Patent No. 2000-213326, an oil return passage for returning the oil which has lubricated a valve train is formed by penetrating a cylinder block. An intermediate portion of the oil return passage bulges downward forming an oil reservoir and a detection unit of a temperature sensor which has been threadedly inserted from a side wall of the cylinder block faces the oil reservoir.
In the above-described system, a timing chain chamber, which is a housing chamber for housing a timing chain for driving a camshaft of a valve train, is formed by penetrating the cylinder block in parallel with the oil return passage. For this reason, there is a drawback that the cylinder block becomes large-sized by a portion corresponding to the oil return passage to be formed, and further the temperature sensor is to be arranged so as to avoid the timing chain chamber having comparatively large width in the circumferential direction with the cylinder axis as the center while excluding interference with and influence of peripheral members to be arranged around the cylinder block such as exhaust pipes. Therefore, layout of the temperature sensor has possibly been restricted.